A wide variety of automated guidance vehicles (AGV) have been developed, for use in an office or industrial environment to perform delivery or work operations. The AGV's track a luminescent guidepath. The guidepath luminesces with a green to yellow color when stimulated with an ultraviolet light incorporated in an AGV's sensor head.
Early versions of the guidepath used on a carpet were made from a fluorescent dye such as benzothiazole derivatives which were dissolved in a non-acidic toluene/methanol solution. This solution worked for light colored carpets such as tan or grey. However, the dye was removed by strong carpet cleaning detergents, and was destroyed by exposure to ultraviolet rays in sunlight.
A second type of carpet guidepath was developed which used toluene as a primary solvent, and again a non-acidic luminescent dye compound such as a benzothiazole derivative, which was not destroyed by sunlight. An acrylic polymer was incorporated into the guidepath formula to bind the dye to the carpet fibers. This guidepath wore away over a few months on most carpets and after repeated applications the material left an unsightly dark line on the surface of the carpet.
A third type of carpet guidepath material was disclosed in U.S. Pat. No. 4,707,297. The neutral to basic material included a fluorescent dye or pigment dispersed in water combined with an acrylic resin crosslinked with zinc or zirconium ions. The guidepath was not visible on carpet and was removable with solutions like ammonia in water. A carpet guidepath made by this method wears away over a three to six month period. This guidepath will also be removed by cleaning with alkaline carpet shampoos.
Alternative systems have been utilized wherein magnetic tapes are being installed beneath the carpet. These systems require no maintenance for the guidepath, however they must be installed before the carpet is put down.
Various other neutral to basic water soluble dyes such as benzothiazole derivatives like sodium 3-(2-benzothiazolyl)-4-hydroxybenzene-sulfonate have been produced and used for guidepaths. The fluorescent emission of these dyes was shifted from green to blue when exposed to these alkaline cleaning materials commonly used in carpet maintenance. The material was also susceptible to discoloration and loss of brightness when exposed to ultraviolet light. Further, the guidepath material's fluorescent emission was not bright enough to be tracked reliably on dark colored carpets.
The present invention provides a guidepath solution of sulfonated luminescent dyes which when applied to carpet in an acid state form a permanent bond between the carpet fiber and the dye. When used in an aqueous solution, the guidepath solution has an adjusted pH below 4.0 and preferably below 2.0. When used in a non-aqueous solution, the acidic dye compound has sulfone groups which are protonated. These compounds luminesce more efficiently, are not affected by conventional alkaline cleaning materials and are not discolored by exposure to ultraviolet radiation.